88 Ranger Right rear tire locks up

[Lowrange2]

If I hit the brakes much at all the RR locks up... Proportioning Valve?

 

[metalmacguyver]

check the adjusters first. make sure that the left and right side are adjusted equally.

 

[rickcdewitt]

i've seen leaky axle seals make a rear wheel lock up. the 90wt makes the brake shoe work way too good.on heavier leaks if you look at the side wall facing in you can see where oil is spun out of the drum onto the tire.

 

[Lowrange2]

I checked for oil on the back plate today and the drum, back plate, and tire is bone dry... not a drop of any kind of fluid. I still haven't pulled the drum yet... thats soon to come.

 

[Wicked_Sludge]

out of adjustment shoes or, more likely, a warped (egg shaped) drum. ford trucks are somewhat notorious for the latter.

 

[Bill]

I checked for oil on the back plate today and the drum, back plate, and tire is bone dry... not a drop of any kind of fluid. I still haven't pulled the drum yet... thats soon to come.

Take the drum off and inspect the shoes and the inside of the drum. It is not possible to inspect the brakes any other way, and chances are just about anything you can think of is speculation at this point.

Any type of liquid could cause this problem, including moisture on some types of linings.

Less likely, a heat-glazed drum or worn linings.

 

[metalmacguyver]

i've seen leaky axle seals make a rear wheel lock up. the 90wt makes the brake shoe work way too good.on heavier leaks if you look at the side wall facing in you can see where oil is spun out of the drum onto the tire.

How does that work? it doesnt make any sense to me. i would think that getting a lubricant on a mechanism thats designed to create friction would have the opposite effect and make it almost impossible for the brakes to work.

 

[MAKG]

It chews up the brake shoes something awful. BTDT.

It also doesn't help that the usual reason for leaky axle seals is a thrashed axle bearing that has cut a significant groove into the shaft (so the brakes are off center).

 

[metalmacguyver]

Btdt?

 

[rickcdewitt]

How does that work? it doesnt make any sense to me. i would think that getting a lubricant on a mechanism thats designed to create friction would have the opposite effect and make it almost impossible for the brakes to work.

my guess is that the burnt byproduct of the 90wt makes the pads grab more

 

[AllanD]

PRoportioning valve? Only if YOU added one rangers don't use them.

SOME early rangers ('83-85) have/had a pressure differential switch that some ignorant people call a proportioning valve, (they can call it a nuclear propultion reactor if they like but that doesn't make it one..)

'86-87 had nothing at all, and starting in '87 SOME Rangers had RABS.

Locking brake on one side but not the other?

I'd look at the side that IS NOT locking and expect to find a seized wheel cylinder.

Out of adjustment brakes would cause both sides to be "Flacid"

AD

 

[Lowrange2]

PRoportioning valve? Only if YOU added one rangers don't use them.

SOME early rangers ('83-85) have/had a pressure differential switch that some ignorant people call a proportioning valve, (they can call it a nuclear propultion reactor if they like but that doesn't make it one..)

'86-87 had nothing at all, and starting in '87 SOME Rangers had RABS.

Locking brake on one side but not the other?

I'd look at the side that IS NOT locking and expect to find a seized wheel cylinder.

Out of adjustment brakes would cause both sides to be "Flacid"

AD

Thanks... I had no idea there was no prop. valve... I guess trouble shooting from my desk doesnt always work... In the past few days the brakes have gone from locking up on one side with little pressure to locking up on both sides with moderate pressure. So now the brakes are more tolerable, it takes more pressure to lock them up... I still havent taken the drums off. I bought shoes to install but now that you said it it seems like the brakes are off center. When I'm stopping the rear end kinda shudders... like it is catching on one spot each time it rotates...

 

[AllanD]

an out of round drum can cause some MAJOR annoying symptoms

The thing most commonly called a proportioning valve is ACTUALLY a "pressure differential switch"
Basically it's a housing with a shuttle valve.
either end of the valve is subjected to pressure from half of the brake
system (typically front and rear circuits) and if one system has a leak
and loses pressure the shuttle valve will move and mechanically trip a
switch that lights a brake system warning light.

Newer vehicles have a common fluid reservoir and a fluid level sensor that
performs the same function.

Now, what'll REALLY drive you nuts is if you have a CRACKED drum...

BTW, the thing that is most commonly MIS-called a "proportioning valve"
is being sold here (by the wrong name of course)

http://cgi.ebay.com/ebaymotors/Mast...ryZ33566QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

This is a pressure differential switch or if you want a descriptive name call it a brake failure warning switch.

"Proportioning" is actually a complex issue of the ratio of master cylinder size relative to caliper bore and rear wheel cylinder bore diameter.

It is fiurther complicated by the fact that the front brakes are not driven directly by pedal pressure, but rather by resistance of a pair of springs inside the master cylinder AND resistance of the rear brake circuit
All that is that is pushed on by the pedal is the REAR HALF of the piston that applies the front brakes.

Simply changing that springs can have a profound effect on brake response relative to pedal pressure.

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[metalmacguyver]

It is fiurther complicated by the fact that the front brakes are not driven directly by pedal pressure, but rather by a spring inside the master cylinder that is pushed on by the piston that applies the rear brakes.

Simply changing that spring can have a profound effect on brake response relative to pedal pressure.

AD

can you go into more detail about this?

 

[AllanD]

It's a lot easier to explain if I'm explaining it to you while you have a master cylinder disassembled in front of you.

The pedal pushrod (or the pushrod from the booster) pushes against the piston that drives the front brakes.
but the "end" of the cylinder is the back end of the piston that drives the rear brakes.

So this piston is doesn't provide pressure for the front brakes directly, because there is a stiff spring between them.
and the front brakes aren't applied until either there is pressure in the rear circuit, OR the spring on the very front of the piston stack starts to compress and provide resistance.

Basically this allows the REAR brakes to apply first before pressure
is applied to the FRONT brakes changing the
stiffness of these springs would change the point where
the front & rear brakes begin to apply...

And just how much rear brake you get...

The REAR brakes are driven by the piston and a single seal pushing against the closed end of the cylinder.

The FRONT brakes OTOH aren't applied until pressure builds in the front chamber (this is opposed by a softer "Return" spring) and that causes the spring between the pistons to collapase.

The thing is that the FRONT "piston" is formed between the back of the REAR piston and the front of the front piston... In other words until that spring between the pistons is compressed NO pressure is applied to the front brakes.

So by applying a stiffer "return" spring up front you an get more front brake but changing the middle spring affects both.
Make that "middle spring" softer you get more front less rear.
Make it stiffer you get more front less rear.

And that is all without changing the bore diameter of the cylinder....

And Ranger Master cylinders came in three bore diameters, 15/16"('87-88) 1" ('89-94) and 1-1/16" ('95-?)

I'm running a '94 1" bore cylinder on an '90 booster with 1997 two-piston calipers. All this in a 1987 truck

The brakes are by my consideration "right" but I'm going to have to start all over again when I swap in an explorer disc axle.


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